1. Field of the Invention
The present invention relates to the field of gas turbines. It relates to a method of operating a gas turbine, in which a gaseous fuel is burned in a combustion chamber and the hot combustion gases which are produced in the process are directed through the gas turbine, and in which method the gaseous fuel is fed to the combustion chamber via a plurality of controllable burners, working in parallel and arranged on one or more concentric, essentially circular rings, and is sprayed into the combustion chamber via fuel holes.
2. Discussion of Background
Gas turbines are being increasingly equipped with multiple burners having a leaner premix technique. In this case, the fuel and the combustion air is premixed as uniformly as possible and is only then fed to the flame. If this is carried out with high excess air, relatively low flame temperatures and thus low nitrogen-oxide formation result.
In accordance with the geometry of gas turbines, the majority of burners are often arranged in an annular shape in the form of annular combustion chambers. EP-0 597 137 B1 and EP-0 597 138 B1, for example, have disclosed such annular combustion chambers. In this case, the liquid or gaseous fuels are fed via fuel-feed rings to the burners arranged in multiple rings, where they are sprayed into the annular combustion chamber and burned. Likewise, the water feed to the burners is ensured via water rings, which are arranged next to the fuel-feed rings.
When gaseous fuel is used, different operating modes of the individual burners may be more or less advantageous depending on the type of loading state, the number of burners in operation, the emission values or similar characteristic quantities of the gas turbine. In the case of double-cone burners, the gaseous fuel, for example in the so-called pilot mode, may be admixed to the combustion air in the center at the base of the double-cone burner through the so-called pilot-gas holes. The burners run in this way are distinguished by a very stable flame with high flame temperature, although this is a factor which also entails disadvantageous emission values. On the other hand, in the so-called premix mode, the gaseous fuel, in double-cone burners, is admixed laterally to the combustion air in the cone region through the premix-gas holes. The flames of burners in the premix mode are distinguished by a low flame temperature and the advantageous emission values associated therewith, but are substantially less stable than burners operated in the pilot mode. A double-cone burner may in principle be constructed in such a way that both of the above operating modes may be run, in succession and in parallel, and the gaseous fuel is accordingly sprayed in through the one or the other set of holes.
If a gas turbine of the type mentioned at the beginning is run up from idling to load operation, undesirable effects often occur. Inter alia, pronounced development of smoke and nitrogen oxide is possible in certain phases of the run-up and at part-load operation, burners may be extinguished, and disadvantageous pulsating of the gas turbine may also occur.
Accordingly, one object of the invention is to provide a novel method and a novel apparatus with which both run-up and part-load operation of a gas turbine operated with gaseous fuel is possible in a reliable, uncomplicated and low-pollution manner.
This object is achieved in a method of the type mentioned at the beginning in that the burners are divided into at least two groups of burners, these groups in each case comprise the burners of one of the rings, and these groups are individually activated as a function of the operating state of the gas turbine. By the use according to the invention of burner groups which can be activated individually with gaseous fuel, the conditions in the combustion chamber can be adapted in an optimum manner to the operating state of the gas turbine, a factor which makes possible run-up and part-load operation under controlled combustion and flow conditions in the gas turbine.
A first preferred embodiment of the method according to the invention is distinguished by the fact that the burners of the gas turbines are ignited and/or started up one after the other in at least two phases, i.e. they are supplied with gaseous fuel. In this case, the start-up is advantageously effected as a function of the speed of the gas turbine, of the load applied to the gas turbine, or of the flue gases emitted by the gas turbine. In addition, the feed of gaseous fuel may be designed to be variable likewise as a function of the abovementioned characteristic quantities. In this way, depending on the basic conditions, an optimum combustion behavior of the annular combustion chamber can be set in a simple manner.
A preferred development of this embodiment is distinguished by the fact that the abovementioned groups, in their arrangement, differ at least partly in their operating mode, i.e. that certain burners are operated in several different operating modes. In particular, division into premix mode and pilot mode permits an extremely suitable setting of the combustion behavior in the annular combustion chamber, and this setting allows the compromise between the prevention of the formation of smoke and nitrogen oxide and flames which are nonetheless stable and safe from extinction to be regulated in an optimum manner.
If the gas turbine is run up from idling to load or part-load operation, the groups are preferably started up one after the other in different phases of the run-up. In this case, the limits between the different phases are again preferably determined as a function of the speed of the gas turbine, the load applied to the gas turbine, and/or as a function of the emissions given off by the gas turbine.